RESPONSE OF HOT ROLLED Al-Zn-Mg-Cu-(Sc-Zr) ALLOYS TO ANNEALING WITH CONSTANT HEATING RATE

In the present work hot rolled AlZnMgCu alloys with and without Sc,Zr addition were studied. First, the temperature and time of annealing of hot rolling was looking for. Then, precipitation reactions of hot rolled alloys were studied by differential scanning calorimetry and microhardness measurements during annealing from room temperature up to 450 degrees C. These measurements were compared to microstructure development that was observed by scanning electron microscope and by electron backscattered diffraction. The grain size was similar to 20 mu m in the AlZnMgCuScZr and similar to 1000 mu m in the AlZnMgCu alloy. Microstructure observation proved eutectic phase at (sub)grain boundaries. Primary multilayer Al-3(Sc,Zr) particles also precipitated during casting and subsequent cooling in the alloy with Sc,Zr addition. These particles were observed in the alloy with Sc,Zr addition after annealing up to 450 degrees C, too. In the DSC curves the exothermic process at similar to 200 degrees C was observed. Activation energy of the process was calculated. There were observed constant values of microhardness (in accuracy of measurements) during annealing up to 450 degrees C. Higher microhardness values were measured in the alloy with Sc,Zr addition.